"The April/May 2007 edition of Machinist's Workshop did a test of
 penetrating oils where they measured the force required to loosen 
rusty test devices. Buy the issue if you want to see how they did
 the test. The results reported were interesting. The lower the
 number of pounds the better.


Penetrating oil . Average load .. Price per fluid ounce
None ................. 516 pounds .
WD-40 .............. 238 pounds .. $0.25
PB Blaster ......... 214 pounds .. $0.35
Liquid Wrench ... 127 pounds .. $0.21
Kano Kroil ........ 106 pounds .. $0.75
ATF-Acetone mix.. 53 pounds .. $0.10   (* see note)

The ATF-Acetone mix was a 50/50 mix (1 to 1 ratio)."

SDC Forum...

(Note -  This formulation was later corrected to be Power Steering Fluid with 
Acetone). As far as I know or have seen, PSteer fluid is almost the same as ATF,
 but the author of the bit acknowledged that Psteer fluid does not separate from 
Acetone, like ATF does)